1. Technical Field
The present invention relates to an arrangement for activating an emergency brake function for a vehicle in dependence of whether a regular brake function, comprising a first brake circuit and a second brake circuit, is out of order. The invention also relates to a method for such activation of an emergency brake function.
2. Background Art
The transportation of heavy loads, such as that often performed commercially by contractors, can and is frequently performed using vehicles of the articulated hauler type. These types of vehicles may be chosen because of their capabilities to operate with large and heavy loads in areas where there are no roads. Example settings for such implementation include load transport in connection with road and tunnel building, sand pits, mines and similar environments.
These types of articulated haulers are typically constructed with a forward vehicle section, often referred to as the engine unit and including a forward frame that supports an engine and a front wheel axle. Further, haulers of this type normally have a rear vehicle section taking the form of a load-carrying unit including a rear frame that supports two wheel axles, a forward bogie axis and a rear bogie axis. The vehicle is commonly designed for switching between operations using various driving wheel combinations, all six wheels on the three axes being selectively operable as driving wheels, depending on the prevailing operating conditions. An articulated hauler may have a weight in the order of 15-30 metric tons and may be loaded with a payload in the order of 20-35 tons.
In a typical articulated hauler, the frame of the engine unit is connected to the frame of the load-carrying unit by means of a special articulation joint. This joint allows the engine unit and the load-carrying unit to pivot in relation to each other about an imaginary longitudinal axis essentially extending in the longitudinal direction of the vehicle. This articulation joint also allows pivoting about a vertical axis for steering of the vehicle. In this manner, the engine unit and the load-carrying unit are allowed to move substantially independently of each other. This reduces the stress loads acting on the vehicle, especially when operating in difficult or complex terrain.
Normally, an articulated hauler is equipped with a diesel engine and an automatic transmission having, for example, six forward gear ratios and two reverse gear ratios. For braking of the vehicle, an operating brake system is used, preferably of the hydraulic type and divided into two circuits; one circuit intended for the engine unit and another circuit intended for the load-carrying unit. The brake system includes conventional disc brakes arranged for braking the respective wheels. With respect to the transmission, there is normally an integrated retarder; that is, an hydraulic brake device that acts on a turbine shaft of the transmission for braking the vehicle.
During braking of the hauler, the driver uses a brake pedal designed in such a way that when depressed, it initially causes activation of a retarder. When depressed further, the mechanical or operating brakes are also activated and caused to operate in cooperation with the retarder. The reason for first activating the retarder is to help control the high thermal loads affecting the operating brake during mechanical braking. Thus, by primarily using the retarder, or at least initially using the retarder, reduced wear of the operating brake system is achieved and an increased operator braking comfort is also realized.
Such haulers are also often suitably equipped with a separate retarder pedal that, when depressed, will only cause braking by means of the retarder.
Further, the hauler normally includes an additional brake function in the form of a motor-brake that is a typically occurring braking function of diesel engines. A motor-brake is controlled by means of a separate control and includes a throttle that, when actuated, will restrict the flow of exhaust gases from the engine during its exhaust phase. This creates a back pressure in the exhaust system that in turn causes a braking effect.
A further brake function utilized in an articulated dumper includes a parking brake that is commonly arranged for being activated in order to assure that a stationary and parked vehicle will not move. A parking brake of this nature is typically arranged so as to act, when actuated, upon a cardan shaft extending rearwards from the engine to the load-carrying unit. More specifically, such a parking brake conventionally includes a brake caliper acting on a brake disc that is in turn fitted on the cardan shaft. The parking brake can be activated by the driver, preferably through a lever or a control in connection with the driver's seat in the vehicle.
Parking brakes of a spring brake type are also utilized in which a clamping action is caused by a spring force. This type of brake is normally released by means of a compressed air circuit, by the aid of which the spring force can be overcome so as to release the brake. The parking brake receives the compressed air supply from a compressor provided on the vehicle, via a compressed air container and a parking brake valve that are arranged in connection with the previously discussed control which can be activated by the driver.
Beside the general purpose of actuating the parking brake in connection with parking the dumper, there is a requirement for using the parking brake as an emergency brake in case the normal operating brake system should cease to function. More specifically, there can be a requirement for automatic actuation of the parking brake because the driver may not always make a correct determination of when the emergency brake should be used.
A problem can also arise if the parking brake is actuated while driving along because this would result in a sudden retardation of the vehicle's movement, usually with the potential for causing personal injury and/or equipment damage. For this reason, it is desirable to avoid inadvertent activation of the parking brake. A spurious fault, however, such as a broken cable or other simple type system fault in the vehicle's electrical system can also result in a command for actuation of the parking brake being issued, and care should be taken to assure that such unintended actuation commands do not lead to application of the emergency brake when not really intended, necessary and/or could disturb driving of the vehicle.
As such situations should be avoided, there is need for improved systems that prevent the parking brake from being automatically activated when not needed.